The present invention relates to a method and an arrangement to provide efficient transmission of optical information in an optical transmission system.
Optical transmission systems using optical fiber as the optical signal transmission medium are gaining in popularity. This is especially because of optical fiber""s substantial immunity to interference or external influences and its ability to transmit a great number of communications channels in the same physical medium the optical fiber without cross talk between the channels.
Modem optical networks contain a number of different optical devices to manipulate information in the form of optical signals transmitted through a network of optical fiber links. The main design principles of optical networks require versatile processing of optical signals to provide necessary network flexibility. Such processing assumes channel routing, add/drop and switching functions, conversion of optical signals from one to another wavelength channel, amplification of optical signals. etc. For high-speed transmission, the effect of chromatic dispersion plays an important role. It leads to additional receiver penalty due to temporal spreading of optical signals travelling through optical fibers. An optical device that compensates for the dispersion is needed to restore the quality of the optical signal.
Another key element is an optical amplifier, which compensates for optical losses in a transmission link between transmitter and receiver. There are many known different types of optical amplifiers, such as Erbium-doped fiber amplifiers, semiconductor optical amplifiers, Raman amplifiers and optical parametric amplifiers. A number of optical devices can separately perform amplification, wavelength conversion, or dispersion compensation of the optical signal. In U.S. Pat. No. 5,274,495 an optical parametric amplifier is described. The optical amplifier provides phase matching between pump light and signal light. Time spreading of optical pulses due to chromatic dispersion of a transmission fiber can be compensated in a various ways. The most commonly used techniques are based on the dispersion compensation fibers and chirped Bragg gratings.
The present invention solves the problem with the necessity to use many different optical devices to achieve versatile processing of optical signals in an optical transmission system in order to provide network flexibility.
Duplicate optical information at a set of input wavelengths is provided by extracting a set of conjugate copy wavelengths from the set of input wavelengths. The input wavelengths and the conjugate copy wavelengths are used separately to provide network flexibility.
Optical information is sent at a set of input wavelengths through an optical network from a sending site. Optical information is processed at an optical parametric amplifier. The input wavelengths are mixed with an optical pump wavelength in the optical parametric amplifier. A set of optical Conjugate copy wavelengths are extracted from the set of input wavelengths in the optical parametric amplifier. As result, two sets of amplified wavelengths are created the set of amplified conjugate copy wavelengths and the set of amplified input wavelengths. The set of conjugate copy wavelengths separated from the set of input wavelengths. The set of conjugate copy wavelengths is sent to, and received by, a first receiving site.
An object of the invention is to combine several functions into one arrangement to provide an efficient transmission of optical information in order to create network flexibility.
Yet another advantage is the option to use the two sets of wavelengths carrying the same information, for redundancy purposes, and thereby appropriate safety to the system.
Yet another advantage is the possibility to contrary, traditional transponders, to perform wavelength conversion in the optical domain only.
Yet another advantage is that the redundant protection link, can be longer than the main transmission fiber link. If the main fiber breaks, the amplification and dispersion compensation features of the idler channels at the conjugate wavelengths can be used to achieve the desired performance without additional amplifiers and dispersion compensation elements.
The invention will now be described more in detail with reference to exemplifying embodiments thereof and also with reference to accompanying drawings.